Before the battery systems we had the Pentium 4 era, when low drop off point of load regulators became mandatory (or you would had additional heat guns on the board in addition to the processor itself).
You'd be wrong about noise. At 5V for example the 7805 is specced at 45uVrms while the LM317 would be 150uVrms.
Also not all 78xx are created equal. Some of the better specced ones are those from ON Semi. Compare with let's say TI and ST and you'll notice some differences not only in specs but also on the schematic diagram. Apparently some manufacturers made some improvements although they still sell under the generic 78xx name.
---In TekScopes@yahoogroups.com, <mosaicmerc@...> wrote :
The LDOs rise have to do more with battery powered devices and portable
devices. For line powered devices I go with the LM317 series for DC reg.
as it has better regulation/noise spec than the 78xx series and can be
set for anything >1.25V up to 37V with a single ended supply.